Great attention has been paid to wireless power transfer by which a power supply cord and a power transmission cable are not used. Three techniques are known as this wireless power transfer technique, namely power transmission by means of electromagnetic induction, power transmission by means of microwaves and so-called resonance-type power transmission.
For example, Japanese Patent Laying-Open No. 2010-268660 (PTD 1) discloses a contactless power transmission device utilizing a resonance-type power transfer technique. This contactless power transmission device includes a secondary resonant coil receiving, in a contactless manner, electric power output from a primary resonant coil of a power transmission device, and a cooling device cooling a secondary resonant coil.
According to this contactless power transmission device, the secondary resonant coil is cooled by the cooling device, thereby allowing suppression of impedance change in the secondary resonant coil, with the result that the power transfer efficiency can be improved (see PTD 1).